System and methods for CBV diagnostics

ABSTRACT

Methods and systems are provided for diagnosing compressor bypass valve degradation. In one example, a method may include indicating degradation of a compressor bypass valve coupled in a compressor bypass based on intake aircharge temperature measured upstream of a compressor inlet via an air charge temperature sensor.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 14/537,216, entitled “SYSTEM AND METHODS FOR CBV DIAGNOSTICS,”filed on Nov. 10, 2014, now U.S. Pat. No. 9,441,568, the entire contentsof which are incorporated herein by reference for all purposes.

FIELD

The present description relates generally to methods and systems forcontrolling a vehicle engine to diagnose compressor bypass valve (CBV)degradation.

BACKGROUND/SUMMARY

In boosted internal combustion engines, compressed air is delivered tothe engine via a compressor, which may be driven by an exhaust turbine.The air is heated as it is compressed. During certain conditions,pressure may build up at the compressor outlet, leading to compressorsurge. Compressor surge primarily leads to noise, vibration, andharshness (NVH), but can also cause compressor damage. A compressorbypass valve (CBV) may be used to release pressure in turbochargedengines. By doing this, the CBV prevents compressor surge and reduceswear on the turbocharger and engine. The CBV relieves the damagingeffects of compressor surge loading by recirculating the air into theintake upstream of the compressor inlet, increasing the flow rate of airthrough the compressor and reducing the pressure ratio across thecompressor.

A common issue with the CBV is that the valve may become stuck open orclosed, causing performance issues. If the valve is stuck open, it willconstantly bleed boost, which will effect torque delivery anddrivability. If the valve is stuck closed, it is unable to recirculatethe air and pressure builds up, potentially leading to a compressorsurge. Thus, the CBV may be intermittently diagnosed to account forthese issues.

In cases where the compressor bypass valve is stuck open, boost pressuremay not build up even with the wastegate completely closed. Thistriggers an underboost condition. However the reason for underboost maynot be immediately known (e.g., stuck wastegate, stuck bypass valve,leak in the air induction system, etc.) and the problem may be difficultto diagnose.

The inventors herein have recognized the above issues and provide anapproach to at least partly address them. In one example, the issuesdescribed above may be addressed by a method for indicating degradationof a CBV coupled in a compressor bypass based on a comparison of intakeaircharge temperature measured upstream of a compressor inlet and airtemperature directly downstream of a compressor. In this way, a largerdifference in temperature can be measured between ambient air and intakeair to help diagnose the CBV.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example engine system including aCBV and ACT sensor.

FIG. 2 represents a high-level flow chart depicting CBV diagnosticmethods.

FIG. 3 is a graph representing sample conditions for a diagnosis of astuck open valve.

FIG. 4 is a graph representing sample conditions for a diagnosis of astuck closed valve.

DETAILED DESCRIPTION

The following description relates to systems and methods for diagnosingcompressor bypass valve (CBV) degradation with use of an air chargetemperature (ACT) sensor coupled at a junction of a compressor bypassand an air intake passage at a compressor inlet, as shown in the systemof FIG. 1. Methods include engine parameter adjustments to alleviate CBVdegradation. FIG. 2 shows an example method for diagnosing the CBV basedon a comparison of the intake air temperature at the compressor inlet(as measured by the ACT sensor) to a respective threshold. In oneexample, the controller may set a first threshold temperature based onambient air temperature to diagnose if the CBV is stuck open. The firstthreshold may represent current ambient air temperature, which may besubstantially equal to compressor intake air temperature if the CBV isclosed. This is because hot, compressed air is unable to flow back tothe compressor intake and warm up the ambient air if the CBV is closed.Thus, if the compressor inlet air temperature does not meet a conditionrelative to the first threshold (e.g., if the compressor inlet airtemperature is greater than the first threshold), the CBV may beindicated to be stuck open. Likewise, determining a second thresholdbased on boost pressure may assist in diagnosing if the CBV is stuckclosed. The second threshold may represent an estimation of compressorair temperature, which is hotter than ambient air temperature. If asignal is sent to open the CBV and a temperature spike is not measuredby the ACT sensor (e.g., if the temperature measured by the ACT sensoris below the second threshold), the valve may be degraded. FIGS. 3-4represent sample scenarios detailing outcomes and adjustments duringinstances of the CBV being stuck open or closed.

FIG. 1 is a schematic diagram showing an example engine system 100,including an engine 10, which may be included in a propulsion system ofan automobile. The engine 10 is shown with four cylinders 30. However,other numbers of cylinders may be used in accordance with the currentdisclosure. Engine 10 may be controlled, at least partially, by acontrol system including controller 12, and by input from a vehicleoperator 132 via an input device 130. In this example, input device 130includes an accelerator pedal and a pedal position sensor 134 forgenerating a proportional pedal position signal PP. As such, the pedalposition signal may indicate a tip-in (e.g., sudden increase in pedalposition), a tip-out (e.g., sudden decrease in pedal position or releaseof the accelerator pedal), and additional driving conditions.

Each combustion chamber (e.g., cylinder) 30 of engine 10 may includecombustion chamber walls with a piston (not shown) positioned therein.The pistons may be coupled to a crankshaft 40 so that reciprocatingmotion of the piston is translated into rotational motion of thecrankshaft. Crankshaft 40 may be coupled to at least one drive wheel 156of a vehicle via an intermediate transmission system 150. Further, astarter motor may be coupled to crankshaft 40 via a flywheel to enable astarting operation of engine 10.

Combustion chambers 30 may receive intake air from intake manifold 44via intake passage 42 and may exhaust combustion gases via exhaustmanifold 46 to exhaust passage 48. Intake manifold 44 and exhaustmanifold 46 can selectively communicate with combustion chamber 30 viarespective intake valves and exhaust valves (not shown). In someembodiments, combustion chamber 30 may include two or more intake valvesand/or two or more exhaust valves.

Fuel injectors 50 are shown coupled directly to combustion chamber 30for injecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12. In this manner, fuel injector 50provides what is known as direct injection of fuel into combustionchamber 30; however it will be appreciated that port injection is alsopossible. Fuel may be delivered to fuel injector 50 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail.

Intake passage 42 may include throttle 21 having a throttle plate 22 toregulate air flow to the intake manifold. In this particular example,the position (TP) of throttle plate 22 may be varied by controller 12 toenable electronic throttle control (ETC). In this manner, throttle 21may be operated to vary the intake air provided to combustion chamber 30among other engine cylinders. In some embodiments, additional throttlesmay be present in intake passage 42, such as a throttle upstream of thecompressor 60 (not shown).

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system may route a desired portion of exhaust gas from exhaustpassage 48 to intake passage 42 via EGR passage 140. The amount of EGRprovided to intake passage 42 may be varied by controller 12 via EGRvalve 142. Under some conditions, the EGR system may be used to regulatethe temperature of the air and fuel mixture within the combustionchamber. FIG. 1 shows a high pressure EGR system where EGR is routedfrom upstream of a turbine of a turbocharger to downstream of acompressor of a turbocharger. In other embodiments, the engine mayadditionally or alternatively include a low pressure EGR system whereEGR is routed from downstream of a turbine of a turbocharger to upstreamof a compressor of the turbocharger.

Engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 60 arrangedalong intake manifold 44. For a turbocharger, compressor 60 may be atleast partially driven by a turbine 62, via, for example a shaft, orother coupling arrangement. The turbine 62 may be arranged along exhaustpassage 48. Various arrangements may be provided to drive thecompressor. For a supercharger, compressor 60 may be at least partiallydriven by the engine and/or an electric machine, and may not include aturbine. Thus, the amount of compression provided to one or morecylinders of the engine via a turbocharger or supercharger may be variedby controller 12.

Further, exhaust passage 48 may include wastegate 26 for divertingexhaust gas away from turbine 62. Additionally, intake passage 42 mayinclude a compressor bypass valve (CBV) 27 configured to recirculateboosted aircharge from downstream of the compressor 60 and upstream of acondensed air cooler (CAC) 80 to the compressor inlet via a compressorbypass passage 128. For example, wastegate 26 and/or CBV 27 may becontrolled by controller 12 to be opened when a lower boost pressure isdesired. For example, in response to compressor surge or a potentialcompressor surge event, the controller 12 may open the CBV 27 todecrease pressure at the outlet of the compressor 60. This may reduce orstop compressor surge. CBV 27 is positioned in a compressor bypasspassage 128 fluidically coupling the intake passage 42 upstream of thecompressor 60 to the intake passage downstream of the compressor 60.Also included in intake passage 42 is an ACT sensor 121. The ACT sensoris coupled at a junction of the compressor bypass 128 and the intakepassage 42 at the compressor inlet. Additionally or alternatively, theACT sensor 121 may be placed downstream of the junction of thecompressor bypass 128 and the intake passage 42 and upstream of thecompressor 60. The ACT sensor 121 may be controlled by controller 12 tomeasure temperatures to obtain a reference ambient air temperature andan intake air temperature upstream of the compressor during instances ofa valve stuck open or closed (e.g., during tip in and tip out,respectively).

Intake passage 42 may further include charge air cooler (CAC) 80 (e.g.,an intercooler) to decrease the temperature of the turbocharged orsupercharged intake gases. In some embodiments, charge air cooler 80 maybe an air to air heat exchanger. In other embodiments, charge air cooler80 may be an air to liquid heat exchanger. In yet other embodiments, theCAC 80 may be a variable volume CAC. Hot charge air from the compressor60 enters the inlet of the CAC 80, cools as it travels through the CAC,and then exits to pass through the throttle 21 and then enter the engineintake manifold 44. Ambient air flow from outside the vehicle may enterengine 10 through a vehicle front end and pass across the CAC, to aid incooling the charge air.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10 for performing variousfunctions to operate engine 10, in addition to those signals previouslydiscussed, including measurement of inducted mass air flow (MAF) frommass air flow sensor 120; engine coolant temperature (ECT) fromtemperature sensor 112, shown schematically in one location within theengine 10; a profile ignition pickup signal (PIP) from Hall effectsensor 118 (or other type) coupled to crankshaft 40; the throttleposition (TP) from a throttle position sensor, as discussed; andabsolute manifold pressure signal, MAP, from sensor 122, as discussed.Engine speed signal, RPM, may be generated by controller 12 from signalPIP. Manifold pressure signal MAP from a manifold pressure sensor may beused to provide an indication of vacuum, or pressure, in the intakemanifold 44. Note that various combinations of the above sensors may beused, such as a MAF sensor without a MAP sensor, or vice versa. Duringstoichiometric operation, the MAP sensor can give an indication ofengine torque. Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, may produce a predetermined number of equallyspaced pulses each revolution of the crankshaft 40.

Other sensors that may send signals to controller 12 include atemperature and/or pressure sensor 124 at the outlet of the charge aircooler 80, and a boost pressure sensor 126. Other sensors not depictedmay also be present, such as a sensor for determining the intake airvelocity at the inlet of the charge air cooler, and other sensors. Insome examples, storage medium read-only memory 106 may be programmedwith computer readable data representing instructions executable bymicroprocessor unit 102 for performing the methods described below aswell as other variants that are anticipated, but not specificallylisted. Example routines and conditions are explained herein at FIGS.2-4.

Turning now to FIG. 2, a high-level flow chart detailing method 200 foridentifying a CBV degradation and adjustments thereof is presented. Asdescribed above, intake air temperature is compared to a first thresholdto diagnose if the CBV is stuck open, where the first threshold is basedon ambient air temperature. Also described above, intake air temperatureis compared to a second threshold to diagnose if the CBV is stuckclosed, where the second threshold is based on boost pressure. Method200 will be described herein with reference to components and systemsdepicted in FIG. 1, particularly, regarding air intake 42, compressor60, CAC 80, CBV 27, and ACT 121. Method 200 may be carried out bycontroller 12 according to a computer readable media stored thereon. Itshould be understood that the method 200 may be applied to other systemsof a different configuration without departing from the scope of thisdisclosure.

At 202, the method determines if the engine is operating under coldstart conditions. A cold engine start may be defined as an enginetemperature below a predetermined threshold, such as ambienttemperature. If the engine is operating under cold start, then themethod may proceed to 204, however, if the engine is not operating undercold start, then the method may proceed to 208. A non-cold engine startmay be defined as an engine operation (which may or may not include anengine start) where the engine temperature is greater than apredetermined threshold, such as greater than ambient temperature. At204, the method measures the engine temperature against thepredetermined threshold. If the engine temperature is above thethreshold then the method may proceed to 208. If the engine temperatureremains below the threshold, then the method will proceed to 206 anddelay diagnostics until the engine temperature is greater than thethreshold. The method may not be performed at a cold start because theengine temperature rises during this period and as a result, the aircharge temperature (ACT) sensor may not be able to detect ambienttemperature accurately.

At 208, the ACT sensor is monitored during engine idle or low engineairflow conditions following engine warm-up. During idle or low engineflow operation, the boost pressure may be close to ambient pressure.Therefore, no air flows through the CBV regardless of whether the CBV isopen or closed. As a result, an ACT reading at the compressor intake isequal to ambient air temperature during these conditions. At 210, theintake aircharge ambient temperature is measured based on the output ofthe ACT sensor, where the ACT sensor is coupled at a junction of thecompressor bypass and an air intake passage upstream of the compressorinlet. The determining of intake air ambient temperature determines thefirst threshold for a tip in, described below. As an example, the firstthreshold increases as ambient air temperature increases. The method mayproceed to 212.

At 212, the controller determines if a tip-in has occurred. As anexample, tip-in may be determined based on increased boost demand or ifthe tip-in is a tip-in beyond an upper threshold pedal position, e.g.,if the accelerator pedal is depressed past a threshold position. If theanswer is yes, then the method may proceed to 214. If the answer is no,then the method may proceed to 224. 224 and subsequent steps will bediscussed in further detail below. At 214, the method determines a firstthreshold intake aircharge temperature based on ambient air temperature.In one example, the first threshold is current ambient temperature.Further, the first threshold may increase as ambient air temperatureincreases. During instances of high boost demand, it may be desired toclose the CBV in order to route all the intake air through thecompressor to meet the boost demand, providing an opportunity to measureif the CBV is degraded. As an example, if the CBV is closed, compressorintake air temperature will be substantially equal to ambient airtemperature. However, if the CBV is stuck open, air may flow through thecompressor bypass pathway, passing by the ACT sensor before beingdirected through the compressor. Since the compressed air is hotter thanambient temperature, the ACT sensor may indicate a higher temperaturethan ambient temperature when the CBV is open. Therefore, a temperaturehigher than ambient during high torque demand conditions may indicate aCBV is stuck open since a signal has been sent to close the CBV, yet thehot, compressed air is still being recirculated back upstream of thecompressor. At 216, the controller measures an intake air temperaturebased on an ACT sensor output. At 218, the intake air temperature ismeasured against the first threshold. If the intake air temperature isgreater than the first threshold, then the method may continue to 220and indicate degradation of a CBV coupled in a compressor bypass. Asexplained above, during times of tip-in (e.g., high torque) thecontroller will close the CBV in response to boost demand, and all thecompressed air will be directed towards the engine. If intake air ishotter than expected (e.g., greater than the first threshold), it mayindicate that the CBV is stuck open, as the hot, compressed air iscontinually recirculated back to the compressor inlet instead of beingdirected to the engine, and thus CBV degradation is indicated. A CBVthat is stuck open (e.g., a CBV that is unable to partially and/or fullyclose) may cause reduced torque delivery and drivability. Thus, at 222,the controller may adjust engine operating parameters to ameliorate thedegraded CBV. As an example, if the CBV is stuck open, the controllermay close the wastegate to assist compressed air flow to the engine bydirecting more exhaust towards the turbine to ensure there is no torqueloss. In contrast, if the intake air temperature is less than the firstthreshold at 218, then the method may indicate no CBV degradation andmaintain current engine operating parameters at 236. The method mayexit.

In another example, further embodiments may include a continuouslyvariable compressor recirculation valve (CCRV) instead of a CBV. In thecase of a CCRV, a stuck open condition may still be measured duringtip-in, however, the first threshold also accounts for the position ofthe valve. As an example, if the CCRV is 80% closed due to instructionsfrom the controller, determination of the first threshold may accountfor the mixture of ambient air along with the compressed air flowthrough the compressor bypass pathway to the compressor intake.

Returning to 212, if no tip-in has occurred, the method proceeds to 224,where the controller determines if a tip-out has occurred. As anexample, the controller may determine the tip-out based on decreasedboost demand and/or where the tip-out is a tip-out beyond a lowerthreshold pedal position, e.g., a tip-out may be determined if theaccelerator pedal is released from a depressed position. If the tip-outhas not occurred, the method may proceed to 225. At 225, the controllermay indicate no valve degradation and maintain current engine operatingparameters. The method may exit. Alternatively, if it is determined thatthe tip-out has occurred, the method may proceed to 226. At 226, thecontroller determines a second threshold based on a boost pressure. Thesecond threshold may represent the expected temperature at thecompressor outlet and thus the second threshold may depend on thecompressor outlet air temperature (estimated based on boost pressure).The CBV may be signaled to open during tip-outs. During tip-outs, thecontroller may open the CBV to dump boost and prevent compressor surge,resulting in a temperature spike at the ACT sensor from the flow of hot,compressed air to the compressor intake. Thus, the ACT measurements whenthe CBV is open may be similar to compressor outlet air temperature andas a result, substantially equal to the second threshold. If the CBV isstuck closed, a temperature spike is not detected, resulting in an ACTmeasurement below the second threshold, indicating the CBV is stuckclosed. The second threshold increases as the boost pressure increases.As an example, compressed air temperature may be estimated via boostpressure and/or demand, which is based on the tip-out. In general, thesecond threshold is larger than the first threshold due to itsdependence on the temperature of the compressed air.

Once the second threshold is determined, the controller measures anintake air temperature at 228, based on output from the ACT sensor. At230, the intake air temperature is compared to the second threshold.During a tip-out event, the CBV may be commanded open to recirculate airback to the compressor inlet in order to increase flow through thecompressor to avoid surge that otherwise might occur due to the low flowconditions following the tip-out. When the CBV is open, the temperatureof the intake air at the compressor inlet may increase as a result ofthe recirculation of the hot compressed air. Thus, if the intake airtemperature is less than the second threshold, it indicates that hotcompressed air is not flowing back to the compressor intake (e.g., dueto the closed CBV) and the temperature of the intake air is lower thanexpected. As an example, as tip-out occurs and boost demand decreases,the controller opens the CBV and reduces compressed airflow to theengine. If the intake air temperature is below the second threshold, theCBV may be stuck closed and NVH may occur, and the method may proceed to232. At 232 the method includes indicating degradation of the CBVcoupled in a compressor bypass based on intake aircharge temperaturemeasured upstream of a compressor inlet wherein the degradation includesthe CBV being stuck closed. At 234, the controller may adjust engineoperating parameters to alleviate CBV degradation. As an example, if atip-out has occurred and the controller determines CBV degradation, thecontroller may adjust engine operating parameters to increase flowthrough the compressor, such as adjust an exhaust gas recirculation(EGR) rate, adjust a throttle position, or other adjustment.

If the intake air temperature is above the second threshold, thencompressed air is able to flow back to the compressor inlet (e.g., dueto open CBV) and the method may continue to 236. At 236, the controllerindicates no CBV degradation and may maintain current engine operatingparameters. The method may end.

FIG. 2 represents a method detailing diagnosis of a CBV degradationbased on compressor inlet temperature compared to either a firstthreshold based on ambient air temperature or a second threshold basedon boost pressure, for both CBV stuck open or closed, respectively. Thefollowing figures represent example engine conditions when operatingwith a CBV that is stuck open or closed.

In another example, a threshold range may be invoked to determine a CBVdegradation. As one example, diagnosis of a CBV being stuck open mayinclude a maximum threshold range that an ambient temperature mayincrease (e.g., temperature increase of 30° C.) during a method todetermine if the CBV is stuck open. If the ambient air temperatureincreases above this threshold range then the CBV may be indicateddegraded. The CBV degradation may include the CBV being stuck open. As asecond example, diagnosis of the CBV being stuck closed may include thesame maximum threshold, however, if the temperature does not increasebeyond the threshold range during a period of aggressive tip-out thenthe CBV may be degraded. The degradation may include the CBV being stuckclosed.

FIG. 3 represents a plot of graphs depicting an example scenario of atip-in and a CBV that is stuck open. The x-axis represents time and they-axis represents different engine parameters. Graph 302 representspedal position (PP), graph 304 represents measured intake airtemperature (IAT), and graph 306 represents expected IAT for the samplescenario. Graph 308 represents the expected position of the CBV (e.g.,the commanded position) and 310 represents the actual CBV position.

Prior to T1, the PP is neither above a threshold to indicate wide-openthrottle (e.g., tip-in) nor below a threshold to indicate asubstantially closed throttle (e.g., tip-out). As a result, the CBV isopen because the engine does not demand the full amount of compressedair. IAT is substantially equal to an ambient air temperature. At T1,the CBV valve is commanded closed due to an increase in PP, as shown bygraph CBV. As PP increases, the throttle opening is wider and the enginerequests more compressed air (e.g., boost demand increases). In order tofulfill this demand, the controller closes the CBV to disable compressedair bypass to the compressor intake.

After T1 and prior to T2, the PP is increased to a position above athreshold in response to a higher boost, indicating the tip-in is atip-in to wide-open throttle or to an increased torque demand. Thecontroller expects to keep the CBV closed, 308, to provide increasedboost pressure and intake temperature. Since the CBV is expected closed,the controller expects to see an IAT similar to the graph of 306,however, it receives the result of 304 because the actual CBV positionis open. The change in boost demand is responsive to a pedal tip-in,indicating that the compressor bypass valve is stuck open based on theactual temperature being higher than the expected temperature. The CBVis degraded and the degradation includes the CBV being stuck open. Theactual CBV position being stuck open, as shown by graph 310, enables theflow of hot, compressed air back to the intake which raises IAT above afirst threshold based on ambient air temperature. At T2, the controllermay indicate the CBV is degraded.

FIG. 4 represents a plot of graphs depicting a tip-out and a CBV that isstuck closed. The x-axis represents time and the y-axis representsdifferent engine parameters. Graph 402 represents pedal position (PP),graph 404 represents an expected intake air temperature (IAT) and graph406 represents an actual intake air temperature for that scenario. Graph408 depicts expected CBV position and 410 represents the actual CBVposition.

Prior to T1, the PP is neither above a threshold to indicate wide-openthrottle nor below a threshold to indicate a substantially closedthrottle. As a result, the CBV is open because the engine does notdemand the full amount of compressed air compressed by the compressor.IAT is substantially equal to an ambient air temperature. At T1, the CBVvalve is closed due to an increase in PP. As PP increases, the throttleopening is wider and the engine requests more compressed air. In orderto fulfill this demand, the controller closes the CBV to disablecompressed air bypass. After T1 and prior to T2, the PP is increased toa position above a, indicating the tip-in is a tip-in to wide-openthrottle or to an increased torque demand. The controller keeps the CBVclosed to provide maximum boost pressure and intake temperature. Sincethe CBV is closed, IAT remains fairly constant. At T2, PP drops to alevel below a threshold indicating a substantially closed throttle andlower boost condition. A lower boost condition includes a tip-out andthe tip-out is an aggressive tip-out to substantially close thethrottle. Therefore, the controller opens the CBV to decrease compressedair flow to the engine and bypass the compressed air back to thecompressor air intake resulting in an increased IAT, 404. As an example,at low torque or low boost events, the controller may open the CBV toprevent compressor surge. Boost demand is responsive to a pedal tip-out,and decreases as the pedal is released, also signaling to open the CBV.If the CBV is open, 408, a temperature spike is measured, however, sincethe actual CBV position is stuck closed, 410, the temperature remainsfairly constant. The CBV being stuck closed prevents hot, compressed airflow back to the compressor intake and results in an intake airtemperature substantially equal to ambient air temperature. Thus, theIAT is below a second threshold based on boost pressure and at T3 thecontroller may indicate CBV degradation.

In this way, placing the compressor bypass passage inlet downstream ofthe compressor and upstream of the CAC, the hot, compressed air isdelivered back directly to the compressor air intake when the CBV isopen, permitting the ACT sensor to measure a much larger air intaketemperature than ambient temperature. By measuring a larger air intaketemperature, the method's percent error is decreased, providing morereliable data to the controller.

The technical effect of measuring intake air temperature at a compressorintake and measuring it against a threshold based on ambient airtemperature measured at the compressor intake allows the method todiagnose CBV degradation more accurately. As a result of ACT sensorplacement, along with compressor bypass pathway placement, a largertemperature gradient is created between the ambient temperature andintake air temperature when the CBV is open, enabling a largerdiagnostic range to detect CBV degradation accurately.

In an embodiment, method for an engine comprises indicating degradationof a compressor bypass valve coupled in a compressor bypass based onintake aircharge temperature measured upstream of a compressor inlet.The intake aircharge temperature is measured by a temperature sensorcoupled at a junction of the compressor bypass and an air intake passageat the compressor inlet. The method, additionally or alternatively, maycomprise the compressor bypass being configured to recirculate boostedaircharge from downstream of the compressor and upstream of a charge aircooler to the compressor inlet.

Additionally or alternatively, the indicating may include during higherboost conditions, indicating degradation of the compressor bypass valvebased on intake aircharge temperature being higher than a firstthreshold, the first threshold based on ambient temperature. Indicatingdegradation includes indicating the compressor bypass valve is stuckopen when the intake aircharge temperature is higher than the firstthreshold. The higher boost condition includes a tip-in. In response tothe indication of the compressor bypass valve being stuck open, closinga wastegate.

The method, additionally or alternatively, may include the ambienttemperature being measured by the temperature sensor during engine idleconditions following engine warm-up. The indicating, additionally oralternatively, may include during lower boost conditions, indicatingdegradation of the compressor bypass valve based on intake airchargetemperature being lower than a second threshold. The second threshold isbased on boost pressure. The indicating degradation includes indicatingthe compressor bypass valve is stuck closed when the intake airchargetemperature is lower than the second threshold. The lower boostcondition includes a tip-out.

Another method for a boosted engine comprises, indicating degradation ofa compressor bypass valve (CBV) in response to intake airchargetemperature at a compressor inlet being higher than a first thresholdduring a tip-in and indicating degradation of the CBV in response tointake aircharge temperature at the compressor inlet being lower than asecond threshold during a tip-out. The tip-in is a tip-in to beyond anupper threshold pedal position, and wherein the tip-out is a tip-out tobeyond a lower threshold pedal position. The first threshold is based onambient temperature, and the second threshold is based on boost pressureat the tip-out.

The method, additionally or alternatively, may include the firstthreshold increasing as ambient temperature increases, and the secondthreshold increasing as boost pressure increases. The indicating,additionally or alternatively, may include indicating degradation duringtip-in includes indicating the CBV is stuck open and the indicatingdegradation during tip-out includes indicating the CBV is stuck closed.The temperature sensor is positioned at a junction of a compressorbypass and an air intake passage at the compressor inlet, the compressorbypass coupling the intake passage from downstream of a charge aircooler to the compressor inlet.

An embodiment of a system comprises a boosted engine having an airintake passage, an accelerator pedal for receiving an operator boostdemand, an intake compressor, a compressor bypass including a compressorbypass valve recirculating aircharge from downstream of the compressorto a compressor inlet, a temperature sensor coupled at junction of thecompressor bypass and the air intake passage, and a controller withcomputer-readable instructions for indicating degradation of thecompressor bypass valve based on an actual intake air temperaturemeasured at the temperature sensor relative to an expected intake airtemperature, the expected intake air temperature based on the change inboost demand. The compressor is driven by an exhaust turbine, the systemfurther includes a wastegate coupled across the turbine, and wherein thecontroller includes further instructions for closing the wastegate inresponse to the indicating of the compressor bypass valve being stuckopen.

The indicating, additionally or alternatively, may include indicatingthat the compressor bypass valve is stuck open based on the actualtemperature being higher than the expected temperature when the changein boost demand is responsive to a pedal tip-in and indicating that thecompressor bypass valve is stuck closed based on the actual temperaturebeing lower than the expected temperature when the change in boostdemand is responsive to a pedal tip-out.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method for diagnosing a continuously variable compressor bypass valve of an engine, comprising: adjusting the continuously variable compressor bypass valve responsive to operating conditions of the engine; and indicating degradation of the compressor bypass valve coupled in a compressor bypass based on intake aircharge temperature being different then a threshold temperature measured upstream of a compressor inlet, and changing engine operating parameters due to the indication.
 2. The method of claim 1, wherein if the compressor bypass valve is stuck open, changing the engine operating parameters includes close a wastegate valve.
 3. The method of claim 1, wherein if the compressor bypass valve is stuck closed, changing the engine operating parameters includes increasing flow through a compressor.
 4. The method of claim 3, wherein increasing flow through the compressor includes adjusting a throttle position.
 5. The method of claim 3, wherein increasing flow through the compressor includes adjusting an exhaust gas recirculation (EGR) rate.
 6. The method of claim 1, wherein the intake aircharge temperature is measured by a temperature sensor coupled at a junction of the compressor bypass and an air intake passage at the compressor inlet.
 7. The method of claim 1, wherein the compressor bypass is configured to recirculate boosted aircharge from downstream of a compressor and upstream of a charge air cooler to the compressor inlet.
 8. The method of claim 1, wherein the indicating includes, during higher boost conditions, indicating degradation of the compressor bypass valve based on the intake aircharge temperature being higher than a first threshold, the first threshold based on ambient temperature.
 9. The method of claim 8, wherein indicating degradation of the compressor bypass valve includes indicating the compressor bypass valve is stuck open.
 10. The method of claim 8, wherein the ambient temperature is measured by a temperature sensor during engine idle conditions following engine warm-up.
 11. The method of claim 9, wherein the indicating further includes, during lower boost conditions, indicating degradation of the compressor bypass valve based on the intake aircharge temperature being lower than a second threshold.
 12. The method of claim 11, wherein the second threshold is based on boost pressure.
 13. The method of claim 11, wherein indicating degradation of the compressor bypass valve includes indicating the compressor bypass valve is stuck closed.
 14. The method of claim 13, wherein the higher boost conditions include a tip-in, and the lower boost conditions include a tip-out.
 15. The method of claim 13, further comprising, in response to the indication of the compressor bypass valve being stuck open, closing a wastegate.
 16. A method for diagnosing a continuously variable compressor bypass valve of a boosted engine, comprising: during a tip-in, indicating degradation of the continuously variable compressor bypass valve (CBV) in response to intake aircharge temperature at a compressor inlet being higher than a first threshold; and during a tip-out, indicating degradation of the CBV in response to intake aircharge temperature at the compressor inlet being lower than a second threshold, and changing engine operating parameters due to the indication.
 17. The method of claim 16, wherein the tip-in is a tip-in to beyond an upper threshold pedal position, and wherein the tip-out is a tip-out to beyond a lower threshold pedal position.
 18. The method of claim 16, wherein the first threshold is based on ambient temperature, and the second threshold is based on boost pressure at the tip-out.
 19. The method of claim 16, wherein the first threshold increases as ambient temperature increases, and the second threshold increases as boost pressure increases.
 20. The method of claim 16, wherein the indicating degradation during the tip-in includes indicating the CBV is stuck open, and the indicating degradation during the tip-out includes indicating the CBV is stuck closed. 